1. Field of the Invention
The present invention relates to roughness measuring method and apparatus, and particularly relates to roughness measuring method and apparatus which enable measurement based on industrial standards of the surface roughness of a work with no cutoff values specified.
2. Description of the Related Art
A surface roughness measuring apparatus is used for inspecting the finished quality of the surface of a processed work. At this time, inspecting standard values (standard values such as cutoff values, parameters to be evaluated, and tolerance limits for parameter values) are indicated in drawings of instructions for processing the work, and the surface roughness of the work is measured according to these inspecting standard values.
However, selection of cutoff values may be difficult if inspecting standard values are not indicated in the drawing of instructions for processing the work, or a work with the surface shape significantly changed due to secular variation after processing, or a work with no drawings attached thereto such as a purchased product.
Then, in consideration of such cases, industrial standards in various countries are defined such that the magnitudes of parameters (Ra, Rz and RSm) to be evaluated are estimated to select a cutoff value being a sampling length for measurement (ISO 4288, JIS B 0601, etc.).
On the other hand, in a roughness measuring method disclosed in German Patent DE19817406C1, the evaluation length is defined to be five times as large as the cutoff value, and is outputted as an effective evaluation value in the cutoff value if the magnitude of the parameter calculated after the measurement of the evaluation length falls within the range of roughness of the cutoff value.
However, in the roughness measuring method disclosed in German Patent DE19817406C1, one evaluation value calculated in one measurement range is determined as an effective estimation value, thus raising a disadvantage that the reliability of the effective estimation value is low, and therefore the surface roughness of the work cannot be measured accurately.
The present invention has been developed in view of such circumstances, and has as its object the provision of a roughness measuring method and a roughness measuring apparatus enabling the surface roughness of a work with no cutoff values specified to be measured accurately.
For attaining the above-described objects, the present invention is characterized in that a measurement area of surface roughness of a work is specified, the total range of the specified measurement area is measured to obtain measurement data showing the surface roughness of the work, a filter having a plurality of predefined cutoff values is used to calculate a plurality of temporary evaluation values for each evaluation length corresponding to the plurality of cutoff values from the measurement data, thereby obtaining a maximum value of the temporary evaluation values, the maximum value is obtained as an effective evaluation value if the maximum value falls within the roughness range of the cutoff value used at that time, and a different cutoff value is used to obtain an effective evaluation value if the maximum value does not fall within the roughness range of the cutoff value used at that time.
Also, for achieving the above-described objects, the present invention is directed to a roughness measuring apparatus, comprising: a stylus which comes into contact with a surface of a work; a measurement area specifying device which specifies a measurement area of surface roughness of the work; a measurement data obtaining device which moves the stylus across a total range of the measurement area specified by the measurement area specifying device to obtain measurement data showing the surface roughness of the work; a maximum value obtaining device which uses a filter having a plurality of predefined cutoff values to calculate a plurality of temporary evaluation values for each evaluation length corresponding to the plurality of cutoff values from the measurement data obtained by the measurement data obtaining device, thereby obtaining a maximum value of the plurality of temporary evaluation values; and an evaluation value outputting device which obtains the maximum value as an effective value if the maximum value obtained by the maximum value obtaining device falls within a roughness range of the cutoff value used at that time, and uses a different cutoff value to obtain and output an effective evaluation value if the maximum value does not fall within the roughness range of the cutoff value used at that time.
According to the present invention, a measurement area of surface roughness of a work is first specified by a measurement area specifying device. Then, the total range of the specified measurement area is measured by a measurement data obtaining device to obtain measurement data showing the surface roughness of the work. Then, a filter having a plurality of predefined cutoff values is used to calculate a plurality of temporary evaluation values for each evaluation length corresponding to the plurality of cutoff values from the measurement data, and a maximum value is obtained from these temporary evaluation values by a maximum value obtaining device. Then, if the maximum value falls within the range of the cutoff value used at that time, an evaluation value outputting device outputs this maximum value as an effective evaluation value of the roughness of the measurement area. Also, if the maximum value does not fall within the range of the roughness of the cutoff value used at that time, a different cutoff value is used to obtain and output the effective evaluation value.
In this way, in the present invention, since the effective evaluation value is determined from a plurality of evaluation values, reliability of the effective evaluation value is high compared to conventional techniques in which the effective evaluation value is determined by one evaluation value, thus making it possible to measure the surface roughness of the work accurately.